1965 Vintage Andersen Window sash balances

I am looking to replace the sash balancers on this Andersen window. It is all wooden construction with a measurement of 23-3/4" x 40-1/4" for the thermo-pane glass. The existing balancer is marked dd12 33 27 on the corner. The balancer dimensions are 6-5/16"x2-13/16"x3/4". I have more photographs if needed but his web-page wouldn't allow their inclusion. These balance units have galvanized steel shims installed along side them too. Seems a bit strange!

Thank you,